1,720,961 research outputs found
A comparison of failure load for zirconia-ceremics restorations with different zirconia/veneer thickness and cooling rate
Full text linkDept. of Dental Science/석사Objectives: The purpose of the current study was to evaluate the influence of different zirconia coping thicknesses and cooling rates on the failure load of zirconia crowns.
Methods: Forty identical abutment models were milled out of polymethylmethacrylate, and zirconia copings of two thicknesses (0.5 mm or 1.5 mm; n = 20 each) were fabricated using a dental computer-aided design and computer-aided manufacturing system. Zirconia crowns were completed by veneering feldspathic ceramics under different cooling rates (conventional or slow, n = 20 for each cooling rate), resulting four zirconia crown groups (n = 10 per group). Each crown was cemented on the abutment and 300,000 cycles of a 50-N load was applied on the crowns in conjunction with 1263 thermocyclings. After fatigue loading, a static load was applied on each crown until failure using a universal testing machine. The mean failure loads were statistically evaluated with one-way and two-way analysis of variance tests (p = 0.05).
Results: No cohesive or adhesive failure was observed after fatigue loading. The greatest mean failure load occurred in zirconia crowns that had 1.5-mm thick coping and had undergone slow cooling (p < 0.001). Furthermore, six of 10 crowns with the 1.5-mm thick coping in the slow cooling group showed coping fractures. However, no coping fractures occurred in the other groups.
Conclusions: Coping thickness and the cooling rate had a significant influence on the mean failure loads of the zirconia crowns. Under conventional cooling conditions, the mean failure load was not influenced by the coping thickness; however, under slow cooling conditions, the mean failure load was significantly influenced by the coping thickness.
Clinical significance: A thicker coping design or slow cooling after the final firing of the veneer ceramic would be beneficial in reducing the incidence of chipping failure in zirconia crowns. A thicker coping design with slow cooling is therefore recommended to minimize chipping failures.ope
A Broadband PHEMT MMIC Distributed Doubler Using High-Pass Drain Line Topology
No full textA broadband frequency doubler, based on distributed
amplifier techniques, has been designed to operate from
11 to 21 GHz. In order to reject the fundamental signal over a
broadband frequency range, the conventional low-pass drain line
structure was replaced with the high-pass structure. This topology
can suppress fundamental signals over broadband without any
balanced structure so that the chip size can be more compact.
Measured conversion losses of better than 10 dB from 11 to
21 GHz input frequencies are achieved with fundamental signal
rejection better than 12 dB. To the best of our knowledge, this is
the first demonstration of distributed doubler using the high-pass
drain line topology
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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